High-voltage direct-current (“HVDC”) networks are seen as a solution for interconnection of disparate or non-synchronous electricity production sites that have emerged with the development of renewable energies. Such HVDC networks are of particular interest for the transmission and distribution of energy produced by offshore wind-farms. Unlike conventional alternating current technologies, such networks offer lower inline losses and absence of stray network capacitances over long distances. Such networks typically have voltage levels of the order of 50 kV and more.
For point-to-point transmission of electricity, a sectioning may be produced via an end-of-line converter. By contrast, the sectioning can no longer be produced by such a converter in multipoint transmissions. The breaking of the direct current in such networks is a critical issue directly conditioning the feasibility and the development of such networks.
For lower voltage levels, mechanical circuit-breakers break the current by opening. Such a mechanical circuit-breaker generally has two conducting parts that are in mechanical contact when the switch element is closed. Separating these parts breaks the current. These mechanical circuit-breakers have many drawbacks, notably when passed through by high currents.
One drawback arises because the intense electric field between the two conducting parts tends to ionize the air in between. This results in arcing between the two conducting parts when opening the mechanical circuit-breaker. This electrical arc tends to erode the two conducting parts.
Another disadvantage is delay. While the arc exists, current is still flowing. With direct current at high voltage, this arc can be sustained for a not inconsiderable period.
In principle, one could discourage arcing by suitably dimensioning a mechanical circuit-breaker for high direct current voltage applications. However, such a circuit breaker tends to have a long opening delay. This is not so useful when trying to protect the network from, for example, a short circuit.